A probe with some similarity to the above probe is known from EP A 0 261 367. The probe is a mechanical probe which is brought into electrical contact with a test point of an electronic component and an alternating square wave test signal is applied to the test point through a transistor and extracted through a circuit connected to the probe. The transistor which is a field effect transistor applies to the test point the mentioned variable signal, so as to simulate regular operation conditions of the component. Parasitic capacitances within the transistor are likely to introduce some distortion into the amplified square-wave voltage.
In electronic equipment and systems (especially if very complex: by way of nonlimiting example, reference can be made to switching exchanges of telecommunications networks), the need often arises to check the behavior of the equipment and of the system in the presence of particular fault conditions. This check can be carried out not only in the testing phase, but it may be a part of the fault diagnosis and/or identification or of automatic reconfiguration functions which often are provided for in such equipment and systems to ensure that the equipment can still operate (at least in part) even in the presence of faults.
In digital equipment, the types of faults to be actuated or inserted (hereafter the terms "actuation" and "insertion" shall be used as synonyms) at the hardware level generally entail forcing certain points of the equipment to a pre-set signal level, corresponding for example to a logic "0" or to a logic "1". A solution conventionally adopted in the art has thus been to establish, in correspondence with the point to be forced to the pre-set signal level, an electrical connection (usually by means of a jumper) towards the ground level or a given power supply level (+V.sub.cc or-V.sub.cc).
This solution is not particularly easy to be put in practice, also in view of its intrinsically "fixed" nature, once the jumper has been applied, the point involved is constantly maintained at the signal level to which the jumper is connected. Hence, it is not possible to monitor quickly the reaction of the equipment at the moment the fault is inserted and/or, which can be of no less interest, at the moment the fault is eliminated.
To overcome these drawbacks, a solution has been proposed, at least at the experimental level , which entails connecting electrical conductors, coming out of the equipment under test, to the fault insertion points. Such conductors lead to a set of electromechanical switches (such as, typically, relays) which allow the required connections to the reference voltages to be established.
This solution cannot be considered fully satisfactory, for several reasons.
Firstly, it is intrinsically cumbersome. Additionally, the conductors connected to the fault insertion points always disturb the equipment being tested. Thus, the fault conditions simulated for the test do not exactly correspond, from the electrical point of view, to the fault conditions likely to occur in the equipment (this is particularly true when current absorption at the fault point is also to be measured). Further, the conductors disturb the operation of the equipment even under regular service conditions, i.e. when there is no fault actuation.